a. Field of the Invention
The present invention is relevant to percolation leaching of metal or mineral ores. More specifically, the present invention encompasses methods and systems for delivery of leaching solution (e.g., lixiviant) onto the surface of the ore as well as the subsurface of the ore. The subsurface solution delivery systems provide for the delivery of solution at varying depths and varying pressures to the heap, which provides a significant benefit over systems in use today.
b. Background
Heap and dump leaching of gold, copper, uranium, nitrates and other metals and/or minerals has been used commercially on a significant basis since the early 1900s. The method of applying the various leach solutions, predominantly water, water with cyanide, and water with sulfuric acid, has varied greatly over time depending on the local atmospheric conditions and, most importantly, the permeability and physical character of the ore, but has been typically limited to the application of such solutions to the surface of the ore.
Early leaching used simple flooding of the surface with water and/or a water and chemical mixture. With the development of sprinklers, (e.g., RAINBIRD® or equivalent), this type of solution distribution became the common practice. Problems associated with the use of sprinklers are evaporation, heat loss, wind loss, and potential damage to the surface of the heap. The principal sprinkler application today is typically limited to lower pressure, controlled droplet size “wobblers,” such as the Senninger WOBBLER®. This method is mostly used on more competent ores where heat loss, wind loss, evaporation, or ore degradation on the surface are not of significant concern.
Various forms of drip irrigation were developed, primarily in the southwest US in the early to late 1960s, with the use of the Bluebird “needle valves” (controlled dripping) used at the Ranchers' Exploration and Development Corporation's Bluebird mine near Miami, Ariz.; the Bagdad wobblers (surgical tubing of small diameter allowed to “wobble” due to the pressure gradient) used by Bagdad Mining Company near Bagdad, Ariz.; and the small diameter polyethylene or plastic tubing used by Miami Copper, subsequently Cyprus Minerals Corporation, near Miami, Ariz. being early examples of the industrial application of these types of solution delivery systems in the mining business.
In recent times, labyrinth type drippers, such as the types described in U.S. Pat. Nos. 5,005,806, 5,030,279, and 4,960,584, developed primarily for the agricultural industry, have been almost exclusively used in the gold and copper industry where the ore character requires drip irrigation. Experimental evidence at the industrial scale shows that under limited hydraulic conductivity of the surface (natural or otherwise), dripper irrigation results, in many instances, in preferential flow paths which limit reagent delivery at depth which necessarily imposes long-leach cycles and sub-optimal use of water and reagents.
Most recently, the application of heap leaching is being attempted on nickel/cobalt laterite ores and other high clay content ores. Nickel/cobalt laterite and other high clay content ores have a character, due to the very high fines content and the degradation with the high acid consumption, that require special solution application methods to deal with low-permeability ores, operating at a high degree of saturation (moisture content) that limits access to the surface, with potential for loss of control on the solution application associated mainly to the reduction of permeability of the heap surface with time. An additional complication with nickel/cobalt ore and/or other high calcium and magnesium ores is scaling, which also complicates the solution distribution system.
Therefore, there exists a significant need in the art to provide for methods and systems to facilitate efficient leaching of difficult to manage heaps in an economical fashion. One object of the present invention is to provide for improved methods and systems for active heap management through the combination of surface and subsurface delivery of leach solutions to heaps.